Micro droplets show great promise as a new high-throughput technology in chemistry, biochemistry and molecular biology. Micro droplets can be generated at rates in excess of several thousands per second and accurately formulated using minute amounts of small molecules, DNA, proteins or cells. Furthermore, integrated active elements can be used to control individual droplets. With technology for creating, dividing, fusing, interrogating and even sorting micro droplets already developed, one of the main problems to be resolved is how to access their contents.
Droplets are naturally self-contained microreactors that prevent sample loss, diffusion and cross-contamination, general issues that afflict traditional microfluidics. However, the isolated nature of droplets prevents physical access of their contents on-chip. Even though this does not represent a problem for many of the applications that have already been demonstrated, it limits the integration of microdroplets with other platforms. Analytical techniques such as mass spectrometry, capillary electrophoresis or liquid chromatography have been successfully integrated with continuous flow micro fluidic devices, but their integration with microdroplets remains hindered.
Background prior art relating to microdroplets can be found in: K. Ahn, J. Agresti, H. Chong, M. Marquez, D. A. Weitz, Applied Physics Letters 2006, 88, 264105; L. M. Fidalgo, C. Abell, W. T. S. Huck, Lab Chip 2007, 7, 948; Y. -C. Tan, J. S. Fisher, A. I. Lee, V. Cristini, A. P. Lee, Lab Chip 2004, 4, 292; P. S. Dittrich, M. Jahnz, P. Schwille, ChemBioChem 2005, 6, 811; K. Ahn, C. Kerbage, T. P. Hunt, R. M. Westervelt, D. R. Link, D. A. Weitz, Appl. Phys. Lett. 2006, 88, 024104; P. S. Dittrich, K. Tachikawa, A. Manz, Anal. Chem. 2006, 78, 3887; J. Bibette, F. L. Calderon, P. Poulin, Rep. Prog. Phys. 1999, 62, 969; J. S. Eow, M. Ghadiri, A. O. Sharif, T. J. Williams, Chemical Engineering Journal 2001, 84, 173; P. Atten, Journal of Electrostatics 1993, 30, 259; J. G. Kralj, M. A. Schmidt, K. F. Jensen, Lab Chip 2005, 5, 531; C. Priest, S. Herminghaus, R. Seemann, Appl. Phys. Lett. 2006, 89, 134101; “Phase separation of segmented flow by the photocatalytic wettability patterning and tuning of microchannel surface”, Go Takei, Arata Aota, Akihide Hibara, Takehiko Kitamori and Haeng-Boo Kim, Eleventh International Conference on Miniaturized systems for Chemistry and Life Sciences, 7-11 Oct. 2007, Paris, France; and also WO2005/021151, WO2007/081387, US2001/0048637, US2004/0219078, EP1380337, and US2006/0280029.
There therefore remains a need for improved techniques for accessing the contents of microdroplets.